1. Field of the Invention
The present invention relates to heterocyclic derivatives, to pharmaceutical compositions comprising these compounds and to their use in therapy, in particular to their use for the manufacture of a medicament for the treatment or prevention of psychiatric diseases where an enhancement of synaptic responses mediated by AMPA receptors is required.
2. Description of Related Art
L-glutamate is the most abundant excitatory neurotransmitter located in the mammalian central nervous system (CNS). L-glutamate plays a significant role in the control of cognition, mood and motor function and these processes are imbalanced in psychiatric and neurological disorders. The physiological effects of glutamate are mediated through two receptor families, the metabotropic (G-protein coupled) receptors and the ionotropic (ligand-gated ion channels) receptors. The ionotropic receptors are responsible for mediating the fast synaptic response to extracellular L-glutamate. The ionotropic glutamate receptors are separated into three subclasses on the basis of molecular and pharmacological differences and are named after the small molecule agonists which were originally identified to selectively activate them: AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid), NMDA (N-methyl-D-aspartate) and kainate (2-carboxy-3-carboxymethyl-4-isopropenylpyrrolidine). The importance of AMPA receptors in brain physiology is widely recognised and it has been shown that AMPA receptors control the majority of fast excitatory amino acid transmission in the CNS and also contribute to synaptic plasticity playing a role in a variety of physiological processes such as learning and memory. To this end there has been a growing appreciation of the utility of positive allosteric modulators of the AMPA receptor for a variety of clinical indications including schizophrenia, depression and Alzheimer's disease.
AMPA receptor subunits are encoded by four distinct genes (termed GluR1 to 4), each representing proteins of around 900 amino acids. The individual sub-units consist of a large extracellular N-terminal domain, an extracellular ligand binding site for L-glutamate formed by domains designated S1 and S2. The transmembrane domain consists of three transmembrane regions, M1, M3 and M4 together with the re-entrant loop M2. This is then followed by a long intracellular C-terminal domain. All four AMPA receptor subunits contain so-called ‘flip’ and ‘flop’ splice variants which differ in alternate slicing of 38 amino acid encoding exons (differing by less than 10 amino acids) in the S2 extracellular domain. Further heterogeneity of the AMPA receptors results from RNA editing, the most significant being the Q/R site located in the pore region (M2) of the GluR2 subunit. The R variant, which a large proportion of native GluR2 subunits are believed to comprise, is characterised by significantly reduced calcium permeability. A further R/G editing site is located in the S2 domain of GluR2, GluR3 and GluR4 with the G form exhibiting an acceleration in the kinetics of recovery from desensitisation.
The kinetics of desensitisation and deactivation are important functional properties of the AMPA receptor that control the magnitude and duration of the synaptic response to glutamate. The processes of desensitisation and deactivation can be modulated by AMPA receptor positive allosteric modulators that bind remotely from the agonist binding site, yet influence agonist binding, or indeed agonist mediated conformational changes in the receptor associated with gating and/or desensitisation. Consequently there are continued efforts to develop drugs that specifically target these properties and which will have therapeutic potential in the treatment of a wide variety of CNS disorders associated with diminished glutamatergic signalling. These conditions include age-related memory impairment, Alzheimer's Disease, Parkinson's Disease, depression, psychosis, cognitive defects associated with psychosis, attention deficit disorder and attention deficit hyperactivity disorder.
A variety of structural classes of compounds are known which act as AMPA receptor modulators (see G. Lynch, Current Opinion in Pharmacology, 2006, 6, 82-88 for a recent review). For example, there are the so-called benzamide compounds related to aniracetam (see A. Arai et al., J Pharmacol Exp. Ther., 2002, 30, 1075-1085), the benzothiadiazine derivatives such as S-18689 (see B. Pirotte, J. Med. Chem., 1998, 41, 2946-2959) and the biarylpropylsulfonamide derivatives (see P. L. Ornstein et al., J. Med. Chem. 2000, 43, 4354-4358). Another class of AMPA receptor modulators was disclosed in International Patent Applications WO 2005/040110 and WO 2005/070916 which detail various heterocyclic compounds as being of utility as glutamate modulators. Compounds in each of these classes exhibit varying degrees of potentiation of the AMPA receptor.
Sustained AMPA receptor activation, however, is also associated with seizures and other proconvulsant side effects (Yamada K. A., Exp. Opin. Invest. Drugs 2000, 9, 765-777). Consequently there remains a need for further AMPA receptor modulators which have an optimal separation between beneficial therapeutic effects and unwanted neurotoxic effects.
US 2004/171603 A1 discloses heterocyclic compounds indicated to be protein kinase inhibitors useful for the treatment of mycobacterial infections. WO 2005/033102 discloses certain thiophene based compounds indicated to be useful for the treatment of diseases associated with ATP-utilizing enzyme inhibition. WO 2006/044826 discloses further thiophene based heterocyclic compounds useful as anti-tumor agents. None of these publications relate to compounds useful for the treatment or prevention of psychiatric diseases where an enhancement of synaptic responses mediated by AMPA receptors is required.